This invention relates, in general, to electronic components, and more particularly, to sensors.
Mechanical transducers can be micromachined from layers of polysilicon. Some transducers have three overlying layers of polysilicon where the middle layer is movable relative to the other two layers. In the case of a capacitive acceleration transducer, the middle layer is displaced toward one of the other two layers by an acceleration having a vector component along a direction substantially perpendicular to the three layers. This displacement of the middle layer changes the capacitance between the layers, and the change in capacitance is used to measure the magnitude of the acceleration.
However, the substrate supporting the three overlying layers as well as the layers themselves can be deformed by mechanical, thermal, or intrinsic stresses and stress gradients. The deformation can affect many aspects of the transducer including the offset capacitance and the transducer sensitivity to acceleration. The offset capacitance is the capacitance between the layers when there is no acceleration. The transducer sensitivity is a measure of how much the capacitance changes in response to a given acceleration. A change in the offset capacitance or the transducer sensitivity can produce an error in the measurement of acceleration. Extra external circuitry can compensate for some of the changes in the offset capacitance or sensitivity, but the extra external circuitry increases the cost of the accelerometer. Also, the amount of compensation that can be provided by the extra external circuitry is limited.
Accordingly, a need exists for an electronic component for measuring acceleration wherein the electronic component is less sensitive to deformation of the underlying support substrate and of the overlying layers themselves.